Is there a Solid State amp that can satisfy a SET guy?

Ralph, glad to hear about the beta production and perception of their sound. Any guidance you can provide on expected timeline to market, mono/stereo, power, estimated price range for your class D?

The Beta production amps are monoblock, 100 w into 8 ohms and 200 into 4. They have balanced and single-ended inputs. Depending on solutions to supply chain interruptions we might be August or September although we've already shipped the first one. Price is 5100/pair.

Anything anybody does with tubes is simply slow and very colored.

Nonsense! The output section of our amps is 600V/uV. Most solid state amps aren't that fast.


We've been working on our own class D project for the last 4 years which is now in Beta production. Its nice to be able to say that they don't sound significantly different from our tubes amps although they have considerably less distortion (most of it in the case of either amp is lower ordered harmonics). Put another way tube amps can be quite neutral.

Headphones bring an addition bit of clarity that's hard to get with loudspeakers. Current drive is advantageous for headphones, but impractical for loudspeakers.

Are you implying a new design, new build?

@sonetduo   Nelson Pass had some made but then the semiconductor house went belly up. Unlike the Sony and Yamaha devices, you can actually kinda sorta find the Tokin devices... So that's about as close to 'common' with these things as it gets!

Funny that tubes like the 6SN7 that were considered obsolete 55 years ago you can still get brand new, but semiconductors go out of production when the wind changes, and when they're gone, that's pretty much it.

There is a Japanese company making some decently high powered ones, can’t remember their name.

@teo_audio

If you are talking about 'VFETs' (Static Induction Transistors or SITs, are the exact same thing as VFETs FWIW...) then the name is Tokin. But you would have to sort out how to make an amplifier with these devices...

Sound-stage is based on volume (not phase dependent), ear to ear timing cues (also not phase dependent as long as shift is same for both speakers). That also primarily happens much less than 20KHz.


I don't think I have ever read any experiment that shows the ability to differentiate anything but quite significant phase shifts.

@roberttdid

This is all true. However there is a reason that wide bandwidth is a sought-after thing going well back (Stewart Hegeman, designer of the original H/K Citation series, felt wide bandwidth to be quite important). That reason is simply while the ear is insensitive to phase in sine waves, triangle waves and the like, it does use phase information for echo location and so does respond to phase information when a spectrum of frequencies are involved. It also interprets phase shift as a tonal coloration; a change in FR one or two octaves outside of the audio passband can be heard as a tonality in the audio band, with little regard for the loudspeakers involved. I had this demonstrated to me in spades about 30 years ago when I was sorting out an MFA Magus preamp in my shop; the complaint was brightness in the phono. It turned out to have an extra timing constant that set the phono EQ to flat at 50KHz. This was clearly audible as a brightness. By simply removing the components responsible in the EQ network, the RIAA slope was restored (at 50KHz) and the brightness removed. When the RIAA curve was tested using an inverse RIAA network, it was perfectly flat up to 20KHz before and **after** the change. I passed this information back to MFA and they incorporated it into their later production of that preamp.


In high end audio we are always concerned about the nth degree; if you really want to get soundstage right, you need wide bandwidth in the electronics even though the speakers won't reproduce it. And we also want the tonality to be correct; especially in an amplifier with a higher output impedance like an SET its going to have FR errors; it will do it no good if it sounds dark on top due to a rolloff above 20KHz.


Alternatively you can employ enough feedback so that the amplifier can compensate for phase shift in the audio passband. But to do that you need north of 60dB of open loop with good Gain Bandwidth Product and good phase margins, since you'll need to blow off 35dB of that gain (if we are talking about a power amp) with feedback.  This is next to impossible with tube amps and very difficult with traditional solid state designs (to my knowledge the Benchmark is one of the very few to do this). The most common amps that employ this much feedback are self-oscillating class D amps (mostly designed by Bruno Putzeys).

For example, one ’higher power output single tube’ amp has Bandwidth listed as 10Hz through 60kHz.

@david_ten 

Almost any power tube has bandwidth from DC to several MHz at least. We have 40MHz bandwidth in the output section of our amps- we intentionally limit the bandwidth in the voltage amplifier. The real issue is the bandwidth of the output transformer (which we haven't got).


The power bandwidth and the low power bandwidth are two different things BTW. I'm of the opinion that they should be nearly the same. But in many amps they are not- its common for the 1 watt bandwidth to be much wider than the full power bandwidth. So it might be a good idea to get some clarity about what is meant by

Bandwidth listed as 10Hz through 60kHz.

Neither can Class-D because of it's switching frequency and associated output filter to get rid of it, that brings phase shift down into the audio band as this shows in red. https://ibb.co/sjNy1Fq

This statement is false in that it ignores entirely self-oscillating amplifiers which are able to correct for phase shift. All the class D amps designed by Bruno Putzeys can do this. Self oscillating amps have been around for over 15 years.

However, it still does not grab my subjective and emotional senses. Could SS be a more objective and intellectual exercise?

You are touching correctly on something about how audio interacts with the brain. The brain has tipping points- in the case of music, its normally processed in the limbic centers. If the brain picks up on something wrong, it will move the processing to the cerebral cortex! Suddenly the music is less involving. IMO/IME, if you want the emotional involvement (and since music is an art form as old as humans themselves, emotional involvement would seem pretty important) then at least for the time being, you're going to have to deal with tubes.

The posts caught my attention as I am in the middle of choosing a 211 or 845 amp. You’ve allayed the concerns the posts raised.

@atmasphere Can you comment as well? Thanks.

@david_ten   The bigger the SET, the more issues you have with bandwidth. Some of this depends on design, for example the type of amp known as a 'parafeed' can have more bandwidth since DC is kept out of the core of the output transformer. This is why the 300b for the most part has described the upper limit of 'hifi' since getting more than about 7 or 8 watts means that the audio passband is compromised. If you really want to get the soundstage right, the amp needs to have minimal phase shift in the audio regions so it will need bandwidth past 80KHz. Most larger SETs simply can't do that!


Also if you want to get the bass right, you need bandwidth on the bottom end to prevent phase shift from robbing the amp of that impact. The general rule of thumb is 10x the cutoff frequency so to do 20Hz correctly you have to go to 2Hz. Again, most SETs can do that, many struggle to get down to 20Hz without rolling off!

IOW the larger SETs can be regarded as a tradeoff between bandwidth and power. Now as I've mentioned a fair amount, with SETs that do not run feedback (which is the vast majority of them) you really don't want to run them past about 20-25% of their full power rating in order to really be hearing what they do. This means that you really need an efficient speaker. Higher power SETs try to get around this limitation somehow, but IME this is a forlorn hope. So if you need more power, you are far better off getting a moderately powered push-pull amp. The distortion is lower overall, so you get a greater amount of 'usable' power. I put that in quotes because of course you can run an SET past that power limit I mentioned, what happens is you get more distortion and it starts to sound loud. But that is an interaction with the kind of distortion its making (higher ordered harmonics) and the way our ears perceive sound pressure (it uses higher ordered harmonics to gauge sound pressure). A push-pull amp is less likely to do this.

If you've ever read a comment about how 'dynamic' a certain SET is, that comment derived directly from running the amp on a speaker that was not efficient enough to prevent the user from running above that 20-25% power region. Dynamics are supposed to come from the recording, not the amp!! The word 'dynamics' as used by audiophiles usually means 'distortion' and the latter can replace the former in most audiophile conversation without changing the meaning of the sentence in which the change occurred.


Bottom line: I would think twice about a buying a higher powered SET, if getting the music to sound more real is your goal. OTOH no worries if you just want a nice sounding stereo that sounds loud.